Improving Cochlear Implant Performance by Pulse Shaping -A Multidisciplinary Approach

Background: A limiting factor in cochlear implants (CI’s) is the spread of current resulting in broad excitation patterns of spiral ganglion cells. In current CI devices, the electrical pulse has a rectangular biphasic pulse shape. Recent evidence from in vitro studies and our modeling work suggest that an alternative, non-rectangular pulse shape might be more beneficial because it better matches the ion channel dynamics of the spiral ganglion cells.

Objective: To investigate novel, biophysically-inspired electrical pulse shapes with the goal to minimize unwanted neural excitation.

Methods: Seven mice were deafened with neomycin and implanted with a 4-channel array (Bionics Institute, Melbourne). Electrically-evoked Auditory Brainstem Responses (eABR) were recorded in response to non-rectangular and rectangular pulse shapes generated by a dedicated Animal Stimulation Platform (Oticon Medical, Nice) (biphasic pulses with 50 µs/phase, 10 µs interphase gap, monopolar configuration). The phase amplitude of rectangular pulses was constant (0-500µA), while the phase amplitude of non-rectangular pulses ramped from 0 µA and up to 500µA or from up to 500 µA and down to 0 µA. eABR latencies and amplitudes were automatically analyzed.

Results: Preliminary data showed that non-rectangular pulses produced a lower threshold compared to rectangular in terms of charge injected. Non-rectangular and rectangular pulse shapes produced different eABR growth functions expressed in terms of the pulse charge.

Conclusion: Data collected presents first evidence of responses to non-rectangular CI pulse shapes in vivo. The preliminary data supports the hypothesis that non-rectangular pulse shapes can have beneficial properties.